Electron-emitting device, electron-emitting apparatus, image display apparatus, and light-emitting apparatus

ABSTRACT

An electron-emitting device in which the specific capacitance and the drive voltage are reduced, and which is capable of obtaining a finer electron beam by controlling the trajectory of emitted electrons. An electron-emitting portion of an electron-emitting member is positioned between the height of a gate and the height of an anode. When the distance between the gate and a cathode is d; the potential difference at driving the device is V 1 ; the distance between the anode and the substrate is H; and the potential difference between the anode and the cathode is V 2 , then the electric field E 1 =V 1 /d during driving is configured to be within the range from 1 to 50 times E 2 =V 2 /H.

This application is a divisional of U.S. application Ser. No.09/941,780, filed Aug. 30, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron-emitting device, anelectron-emitting apparatus, an electron source and an image-formingapparatus. The present invention also relates to a display apparatussuch as a television broadcast display, a display for use in a videoconference system or a computer display, and to an image-formingapparatus designed as an optical printer using a photosensitive drum orthe like.

2. Related Background Art

A field emission (FE) type of electron-emitting device which emitselectrons from a surface of a metal when a strong electric field of 10⁶V/cm or higher is applied to the metal, and which is one of the knowncold cathode electron sources, is attracting attention.

If the FE-type cold electron source is put to practical use, a thinemissive type image display apparatus can be realized. The FE-type coldelectron source also contributes to reductions in power consumption andweight of an image display apparatus.

FIG. 13 shows a vertical FE-type cold electron source structure formedof a substrate 131, an emitter electrode 132, an insulating layer 133,an emitter 135, and an anode 136. The shape of an electron beam withwhich the anode is irradiated is indicated by 137. This structure is ofa Spindt type such that an opening is formed in the insulating layer 133and the gate electrode 134 provided on the cathode 132, and the emitter135 having a conical shape is placed in the opening. (This type ofstructure is disclosed by, for example, C. A. Spindt, “PhysicalProperties of thin-film field emission cathodes with molybdenum cones”,J. Appl. Phys., 47, 5248 (1976).)

FIG. 14 shows a lateral FE structure formed of a substrate 141, anemitter electrode 142, an insulating layer 143, an emitter 145, and ananode 146. The shape of an electron beam with which the anode isirradiated is indicated by 147. The emitter 145 having an acute extremeend and the gate electrode 144 for drawing out electrons from theextreme end of the emitter are disposed above and parallel to thesubstrate, and the collector (anode) is formed above the gate electrodeand the emitter electrode remote from the substrate (see U.S. Pat. Nos.4,728,851, 4,904,895, etc.).

Also, Japanese Patent Application Laid-open No. 8-115652 discloses anelectron-emitting device using fibrous carbon which is deposited in anarrow gap by performing thermal cracking of an organic chemicalcompound gas on a catalyst metal.

In an image display apparatus using one of the above-described FE-typeelectron sources, an electron beam spot is obtained which has a size(hereinafter referred to as “beam diameter”) depending on the distance Hbetween the electron source and the phosphor, the anode voltage Va, andthe device drive voltage Vf. The beam diameter is smaller than amillimeter and the image display apparatus has sufficiently highresolution.

In recent years, however, there has been a tendency to require higherresolution of image display apparatuses.

Further, with the increase in the number of display pixels, powerconsumption during driving due to the device capacitance ofelectron-emitting devices is increased. Therefore there is a need toreduce the device capacitance and the drive voltage and to improve theefficiency of electron-emitting devices.

In the above-described Spindt type of electron source, the gate islaminated on the substrate with the insulating layer interposedtherebetween, so that parasitic capacitances are produced between largecapacitances and a multiplicity of emitters. Moreover, the drive voltageis high, several ten to several hundred volts, and capacitive powerconsumption is disadvantageously large because of the specificstructure.

Also, since the beam of electrons drawn out spreads out, there is a needfor a focusing electrode for limiting spreading of the beam. Forexample, Japanese Patent Application Laid-open No. 7-6714 discloses amethod of converging electron trajectories by disposing an electrode forfocusing electrons. This method, however, has the problem of an increasein complexity of the manufacturing process, a reduction in electronemission efficiency, etc., due to the addition of the focusingelectrode.

In ordinary lateral FE electron sources, electrons emitted from thecathode are liable to impinge on the opposed gate electrode. Thereforethe structure of lateral FE electron sources has the problem of areduction in the efficiency (the ratio of the electron current flowingthrough the gate and the electron current reaching the anode) andconsiderable spreading of the beam shape on the anode.

SUMMARY OF THE INVENTION

In view of the above-described problems, an object of the presentinvention is to provide an electron-emitting device in which thespecific capacitance is reduced, which has a lower drive voltage, andwhich is capable of obtaining a finer electron beam by controlling thetrajectory of emitted electrons.

To achieve the above-described object, according to one aspect of thepresent invention, there is provided an electron-emitting apparatuscomprising:

a first electrode and a second electrode disposed on a surface of asubstrate;

first voltage application means for applying to the second electrode apotential higher than a potential applied to the first electrode;

an electron-emitting member disposed on the first electrode;

a third electrode disposed so as to face the substrate, electronsemitted from the electron-emitting member reaching the third electrode;and

second voltage application means for applying to the third electrode apotential higher than each of the potentials applied to the first andsecond electrodes, wherein a surface of the electron-emitting member isplaced between a plane containing a surface of the second electrode andsubstantially parallel to the surface of the substrate and a planecontaining a surface of the third electrode and substantially parallelto the surface of the substrate. When the distance between the secondelectrode and the first electrode is d; the potential difference appliedbetween the second electrode and the first electrode by the firstvoltage application means is V1; the distance between the thirdelectrode and the substrate is H; and the potential difference betweenthe potential applied to the third electrode by the second voltageapplication means and the potential applied to the first electrode bythe first voltage application means is V2, then an electric fieldE1=V1/d is within the range from 1 to 50 times an electric fieldE2=V2/H.

According to another aspect of the present invention, there is providedan electron-emitting apparatus comprising:

a first electrode and a second electrode disposed on a surface of asubstrate;

first voltage application means for applying to the second electrode apotential higher than a potential applied to the first electrode;

a plurality of fibers disposed on the first electrode, the fiberscontaining carbon as a main ingredient;

a third electrode disposed so as to face the substrate, electronsemitted from the fibers reaching the third electrode; and

second voltage application means for applying to the third electrode apotential higher than each of the potentials applied to the first andsecond electrodes, wherein a surface region of the fibers is placedbetween a plane containing a surface of the second electrode andsubstantially parallel to the surface of the substrate and a planecontaining a surface of the third electrode and substantially parallelto the surface of the substrate.

In the above-described arrangement, the place at which the electricfield concentrates is limited to one side of the region where an emittermaterial is formed, thereby enabling emitted electrons to be first drawnout toward the extraction electrode (gate electrode) and then made toreach the anode with substantially no possibility of impinging on theextraction electrode. As a result, the electron emission efficiency isimproved. Also, there is substantially no possibility of scattering ofelectrons on the extraction electrode, so that the size of the beam spotobtained on the anode is smaller than that in the conventional devicehaving the problem of scattering on the extraction electrode.

According to still another aspect of the present invention, there isprovided an electron-emitting device comprising:

a fiber containing carbon as a main ingredient; and

an electrode for controlling emission of electrodes from the fibercontaining carbon as a main ingredient, wherein the fiber containingcarbon as a main ingredient has a plurality of layered (laminated)graphenes so as not to be parallel to the axis direction of the fiber.

According to a further aspect of the present invention, there isprovided an electron-emitting device comprising:

a first electrode and a second electrode disposed on a surface of asubstrate, a gap being formed between the first and second electrodes;and

a fiber provided on the first electrode, the fiber containing carbon asa main ingredient, wherein the second electrode comprises an electrodefor controlling emission of electrons from the fiber containing carbonas a main ingredient, and wherein the fiber containing carbon as a mainingredient comprises graphene.

The electron-emitting device of the present invention can stably emitelectrons in a low vacuum degree at an increased rate for a long timeperiod.

According to the present invention, a light-emitting member is providedon the anode in the electron-emitting apparatus or above theelectron-emitting device to form a light-emitting device, an imagedisplay apparatus or the like capable of operating in a low vacuumdegree and effecting high-luminance emission/display for a long timeperiod with stability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing an example of a basicelectron-emitting device in accordance with the present invention;

FIGS. 2A and 2B are diagrams showing a second embodiment of the presentinvention;

FIGS. 3A and 3B are diagrams showing a third embodiment of the presentinvention;

FIGS. 4A and 4B are diagrams showing a fourth embodiment of the presentinvention;

FIGS. 5A, 5B, 5C, and 5D are diagrams showing fabrication steps in afirst embodiment of the present invention;

FIG. 6 is a diagram showing an arrangement for operating theelectron-emitting device of the present invention;

FIG. 7 is a diagram showing an operating characteristic of the basicelectron-emitting device of the present invention;

FIG. 8 is a diagram showing an example of the configuration of a passivematrix circuit using a plurality of electron sources in accordance withthe present invention;

FIG. 9 is a diagram showing an example of the construction of an imageforming panel using the electron source of the present invention;

FIG. 10 is a diagram showing an example of a circuit for the imageforming panel using the electron source of the present invention;

FIG. 11 is a diagram schematically showing the structure of a carbonnanotube;

FIG. 12 is a diagram schematically showing the structure of a graphitenanofiber;

FIG. 13 is a diagram showing a conventional vertical FE structure; and

FIG. 14 is a diagram showing an example of a conventional lateral FEstructure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings. The description ofcomponents of the embodiments made below with respect to the size,material and shape of the components and the relative positions of thecomponents is not intended to limit the scope of the present inventionexcept for particular mention of specified details.

The operating voltage Vf of FE devices is generally determined by theelectric field at an extreme end of an emitter obtained from the Poissonequation and by the current density of electron emission currentaccording to the relational expression called “Fowler-Nordheim equation”with a work function of the electric field and the emitter portion usedas a parameter.

A stronger electric field is obtained as the electric field necessaryfor emission of electrons as the distance D between the emitter extremeend and the gate electrode is smaller or the radius r of the emitterextreme end is smaller.

On the other hand, the maximum size Xd in the X-direction of theelectron beam obtained on the anode (e.g., the maximum reach from thecenter of the circular beam shape 137 shown in FIG. 13) is expressed insuch a form as to be proportional to (Vf/Va) in simple calculation.

As is apparent from this relationship, an increase in Vf results in anincrease in beam diameter.

Consequently, there is a need to minimize the distance D and the radiusof curvature r in order to reduce Vf.

Beam shapes in conventional arrangements will be described withreference to FIGS. 13 and 14. In FIGS. 13 and 14, substrates which arecorresponding components of the two arrangements are indicated by 131and 141; emitter electrodes by 132 and 142; insulating layers by 133 and143; emitters by 135 and 145; anodes by 136 and 146; the shapes ofelectron beams with which the anodes are irradiated by 137 and 147.

In the case of the Spindt type described above with reference to FIG.13, when Vf is applied between the emitter 135 and the gate 134, thestrength of the electric field at the extreme end of the projection ofthe emitter 135 is increased and electrons are thereby taken out of aconical emitter portion about the extreme end into the vacuum.

The electric field at the extreme end of the emitter is formed based onthe shape of the extreme end of the emitter to have a certain finitearea on the same, so that electrons are perpendicularly drawn out fromthe finite emitter extreme end area according to the potential.

Simultaneously, other electrons are emitted at various angles. Electronsemitted at larger angles are necessarily drawn toward the gate.

As a result, if the gate is formed so as to have a circular opening, thedistribution of electrons on the anode 136 shown in FIG. 13 forms asubstantially circular beam shape 137. That is, the shape of the beamobtained is closely related to the shape of the drawing gate and to thedistance between the gate and the emitter.

In the case of the lateral FE electron source (FIG. 14) in whichelectrons are drawn out generally along one direction, an extremelystrong electric field substantially parallel to the surface of thesubstrate 141 (lateral electric field) is produced between the emitter145 and the gate 144, so that part 149 of electrons emitted from theemitter 145 are drawn into the vacuum above the gate 144 while the otherelectrons are taken into the gate electrode 144.

In the arrangement shown in FIG. 14, electric field vectors toward theanode 146 differ in direction from those causing emission of electrons(the electric field from the emitter 145 toward the gate 144). Thereforethe distribution of electrons (beam spot) formed by emitted electrons onthe anode 146 is increased.

The electric field of electrons drawn out from the emitter electrode 145(referred to as “lateral electric field” in the following descriptionfor convenience sake while the electric field strengthening effect ofthe emitter configuration is ignored) and the electric field toward theanode (referred to as “vertical electric field” in the followingdescription) will further be described.

The “lateral electric field” can also be expressed as “electric field ina direction substantially parallel to the surface of substrate 131(141)” in the arrangement shown in FIG. 13 or 14. It can also beexpressed as “electric field in the direction of opposition of gate 144and emitter 145” with respect to the arrangement shown in FIG. 14 inparticular.

Also, the “vertical electric field” can also be expressed as “electricfield in a direction substantially perpendicular to the surface ofsubstrate 131 (141)” in the arrangement shown in FIG. 13 or 14, or as“electric field in the direction in which the substrate 131 (141) isopposed to the anode 136 (146)”.

In the arrangement shown in FIG. 14, as described above, electronsemitted from the emitter are first drawn out by the lateral electricfield, fly toward the gate, and are then moved upward by the verticalelectric field to reach the anode.

Important factors of this effect are the ratio of the strengths of thelateral and vertical electric fields and the relative position of theelectron emission point.

When the lateral electric field is stronger than the vertical electricfield by an order of magnitude, the trajectories of almost all ofelectrons drawn out from the emitter are gradually bent by radialpotential produced by the lateral electric field so that the electronsfly toward the gate. A part of the electrons impinging on the gateejects again in a scattering manner. After ejection, however, theelectrons repeat scattering while spreading out along the gate byforming elliptical trajectories again and again and while being reducedin number when ejecting until they are caught by the vertical electricfield. Only after the scattered electrons have exceeded an equipotentialline formed by the gate potential (which line may be called “stagnationpoint”), they are moved upward by the vertical electric field.

When the lateral electric field and the vertical electric field areapproximately equal in strength, the restraint imposed by the lateralelectric field on electrons drawn out is reduced, although thetrajectories of the electrons are bent by the radial potential. In thiscase, therefore, electron trajectories appear along which electronstravel to be caught by the vertical electric field without impinging onthe gate.

It has been found that if the electron emission position at whichelectrons are emitted from the emitter is shifted from the gate planetoward the anode plane (see FIG. 6), emitted electrons can formtrajectories such as to be caught by the vertical electric field withsubstantially no possibility of impinging on the gate when the lateralelectric field and the vertical electric field are approximately equalin strength, that is, the ratio of the strength of the lateral electricfield to that of the vertical electric field is approximately 1 to 1.

Also, a study made of the electric field ratio has shown that if thedistance between the gate electrode 144 and the extreme end of theemitter electrode 145 is d; the potential difference (between the gateelectrode and the emitter electrode) when the device is driven is V1;the distance between the anode and the substrate (element) is H; and thepotential difference between the anode and the cathode (emitterelectrode) is V2, a trajectory along which electrons drawn out impingeon the gate is formed when the lateral electric field E1 V1/d is 50times or more stronger than the vertical electric field E2=V2/H.

The inventor of the present invention has also found that a height s(defined as the distance between a plane containing a portion of a gateelectrode 2 surface and substantially parallel to a substrate 1 surfaceand a plane containing an electron-emitting member 4 surface andsubstantially parallel to the substrate 1 surface (see FIG. 6)) can bedetermined such that substantially no scattering occurs on the gateelectrode 2. The height s depends on the ratio of the vertical electricfield and the lateral electric field (vertical electric fieldstrength/lateral electric field strength). As the vertical-lateralelectric field ratio is lower, the height s is lower. AS the lateralelectric field is stronger, the necessary height s is higher.

The height set in a practical manufacturing process ranges from 10 nm to10 μm.

In the conventional arrangement shown in FIG. 14, the gate 144 and theemitter (142, 145) are formed flush with each other along a common planeand the lateral electric field is stronger than the vertical electricfield by an order of magnitude, so that there is a considerable tendencyto reduce, by impingement on the gate, the amount of electrons drawn outinto the vacuum.

Further, in the conventional arrangement, the structure of the device isdetermined so as to increase the strength of the electric field in thelateral direction, so that the electron distribution on the anode 146spreads widely.

As described above, to restrict the distribution of electrons reachingthe anode 146, it is necessary (1) to reduce the drive voltage (Vf), (2)to unidirectionally draw out electrons, (3) to consider the trajectoryof electrons and, if scattering on the gate occurs, (4) to consider theelectron scattering mechanism (elastic scattering in particular).

Therefore the present invention aims to provide an electron-emittingdevice in which the distribution of electrons with which the anodesurface is irradiated is made finer, and in which the electron emissionefficiency is improved (the amount of emitted electrons absorbed in thegate electrode is reduced).

The structure of a novel electron-emitting device in accordance with thepresent invention will now be described below in detail.

FIG. 1A is a schematic plan view showing an example of anelectron-emitting device in accordance with the present invention. FIG.1B is a cross-sectional view taken along the line 1B-1B of FIG. 1A. FIG.6 is schematic cross-sectional view of the electron-emitting apparatusof the present invention in a state where the electron-emittingapparatus having an anode disposed above the electron-emitting device ofthe present invention is being driven.

In FIGS. 1A, 1B and 6 are illustrated an insulating substrate 1, anextraction electrode 2 (also referred to as “gate electrode” or “secondelectrode”), a cathode 3 (also referred to as “first electrode”), anelectron-emitting material 4 provided on the cathode 3 (also referred toas “electron-emitting member” or “emitter material”), and an anode 61(also referred to as “third electrode”).

In the electron-emitting apparatus of the present invention, if as shownin FIGS. 1A, 1B and 6 the distance by which the cathode 3 and the gateelectrode 2 are spaced apart from each other is d; the potentialdifference (the voltage between the cathode 3 and the gate electrode 2)when the electron-emitting device is driven is Vf; the distance betweenthe anode 61 and the surface of the substrate 1 on which theelectron-emitting device is arranged is H; and the potential differencebetween the anode 61 and the cathode 3 is Va, an electric field producedto drive the device (lateral electric field): E1=Vf/d is set within therange from 1 to 50 times an electric field between the anode and thecathode (vertical electric field): E2=Va/H.

The proportion of electrons impinging on the gate electrode 2 inelectrons emitted from the cathode 3 is reduced thereby. In this manner,a high-efficiency electron-emitting device capable of preventing anemitted electron beam from spreading out widely can be obtained.

The “lateral electric field” referred to in the description of thepresent invention can also be expressed as “electric field in adirection substantially parallel to the surface of substrate 1”. It canalso be expressed as “electric field in the direction in which the gate2 is opposed to the cathode 3”.

Also, the “vertical electric field” referred to in the description ofthe present invention can also be expressed as “electric field in adirection substantially perpendicular to the surface of substrate 1”. Itcan also be expressed as “electric field in the direction in which thesubstrate 1 is opposed to the anode 61”.

Further, in the electron-emitting apparatus of the present invention, aplane containing the surface of the electron-emitting member 4 andsubstantially parallel to the surface of the substrate 1 is spaced apartfrom a plane containing a portion of the surface of the gate electrode 2and substantially parallel to the surface of the substrate 1 (see FIG.6). In other words, in the electron-emitting apparatus of the presentinvention, a plane containing the surface of the electron-emittingmember 4 and substantially parallel to the surface of the substrate 1 isplaced between the anode 61 and a plane containing a portion of thesurface of the gate electrode 2 and substantially parallel to thesubstrate surface (see FIG. 6).

Further, in the electron-emitting device of the present invention, theelectron-emitting member 4 is placed at a height s (defined as thedistance between the plane containing a portion of the surface of gateelectrode 2 and substantially parallel to the surface of substrate 1 andthe plane containing the surface of electron-emitting member 4 andsubstantially parallel to the surface of substrate 1 (see FIG. 6)) suchthat substantially no scattering occurs on the gate electrode 2.

The height s depends on the ratio of the vertical electric field and thelateral electric field (vertical electric field strength/lateralelectric field strength). As the vertical-lateral electric field ratiois lower, the height s is lower. As the lateral electric field isstronger, the necessary height s is higher. Practically, the height isnot less than 10 nm not more than 10 μm.

Examples of the insulating substrate 1 are the following substrateswhose surfaces are sufficiently cleansed: quartz glass; glass in whichthe content of an impurity such as Na is reduced by partial substitutionby K, for example; a laminate formed in such a manner that SiO₂ islaminated by sputtering or the like on soda lime glass, a siliconsubstrate or the like; and an insulating substrate made of a ceramicsuch as alumina.

Each of the extraction electrode 2 and cathode 3 is an electricallyconductive member formed on the surface of the substrate 1 by anordinary vacuum film forming technique, such as evaporation orsputtering, or a photolithography technique so as to face each other.The material of the electrodes 2 and 3 is selected from, for example,carbon, metals, nitrides of metals, carbides of metals, borides ofmetals, semiconductors, and metallic compounds of semiconductors. Thethickness of the electrodes 2 and 3 is set within the range from severalten nanometers to several ten microns. Preferably, the material of theelectrodes 2 and 3 is a heat resistant material formed of carbon, ametal, a nitride of a metal or a carbide of a metal.

The material of the electrodes 2 and 3 constituting theelectron-emitting device in accordance with the present invention aredisposed on the surface of the substrate 1. Needless to say, theextraction electrode 2 and the cathode 3 are spaced apart from eachother along a direction substantially parallel to the plane containingthe surface of the substrate 1. In other words, the electron-emittingdevice is constructed so that the extraction electrode 2 and the cathode3 do not overlap each other.

In particular, in the case of growth of fibrous carbon described below,the electrodes are preferably formed of silicon having conductivity,e.g., doped polysilicon or the like.

If there is apprehension about, for example, a voltage drop due to thesmall thickness of the electrodes, or if a plurality of theelectron-emitting devices are used in matrix form, a low-resistancewiring metallic material may be used to form suitable wiring portions oncondition that it does not affect emission of electrons.

The emitter material (electron-emitting member) 4 may be formed in sucha manner that a film deposited by an ordinary vacuum film forming methodsuch as sputtering is worked into the shape of the emitter by using atechnique such as reactive ion etching (RIE). Alternatively, it may beformed by growing needle crystals or whiskers by seed growth in chemicalvapor deposition (CVD). In the case of RIE, the control of the emittershape depends on the kind of the substrate used, the kind of gas, thegas pressure (flow rate), the etching time, the energy for formingplasma, etc. In a CVD forming process, the emitter shape is controlledby selecting the kind of the substrate, the kind of gas, the flow rate,the growth temperature, etc.

Examples of the material used to form the emitter (electron-emittingmember) 4 are carbides, such as TiC, ZrC, HfC, TaC, SiC, and WC,amorphous carbon, graphite, diamondlike carbon, carbon containingdispersed diamond, and carbon compounds.

According to the present invention, fibrous carbon is particularlypreferably used as the material of the emitter (electron-emittingmember) 4. “Fibrous carbon” referred to in the description of thepresent invention can also be expressed as “material in columnar formcontaining carbon as a main constituent” or “material in filament formcontaining carbon as a main constituent”. Further, “fibrous carbon” canalso be expressed as “fibers containing carbon as a main constituent”.More specifically, “fibrous carbon” in accordance with the presentinvention comprises carbon nanotubes, graphite nanofibers, and amorphouscarbon fibers. In particular, graphite nanofibers are most preferred aselectron-emitting member 4.

The gap between the extraction electrode 2 and the cathode 3 and thedrive voltage (the voltage applied between the extraction electrode 2and the cathode 3) may be determined so that the value of the lateralelectric field necessary for emission of electrons from the cathodematerial used is 1 to 50 times larger than that of the vertical electricfield necessary for forming an image, as described above.

In a case where a light-emitting member such as a phosphor is providedon the anode, the necessary vertical electric field is, preferably,within the 10⁻¹ to 10 V/μm range. For example, in a case where the gapbetween the anode and the cathode is 2 mm and 10 kV is applied betweenthe anode and the cathode, the vertical electric field is 5 V/μm. Inthis case, the emitter material (electron-emitting member) 4 to be usedhas an electron-emitting electric field value of 5 V/μm or higher. Thegap and the drive voltage may be determined in correspondence with theselected electron-emitting electric field value.

An example of a material having an electric field threshold of severalV/μm is fibrous carbon. Each of FIGS. 11 and 12 shows an example of theconfiguration of fibrous carbon. In each of FIGS. 11 and 12, theconfiguration is schematically shown at the optical microscope level (to1,000 times) in the left-hand section, at the scanning electronmicroscope level (to 30,000 times) in the middle section, and at thetransmission electron microscope level (to 1,000,000 times) in theright-hand section.

A graphene structure formed into a cylinder such as that shown in FIG.11 is called a carbon nanotube (a multilayer cylindrical graphenestructure is called a multiwall nanotube). Its threshold value isminimized when the tube end is opened.

The fibrous carbon shown in FIG. 12 may be produced at a comparativelylow temperature. Fibrous carbon having such a configuration is composedof a graphene layered body (thus, it may be referred to as “graphitenanofiber”, and has an amorphous structure whose ratio is increased withtemperature). More specifically, “graphite nanofiber” designates afibrous substance in which graphenes are layered (laminated) in thelongitudinal direction thereof (in the axis direction of the fiber). Inother words, graphite nanofiber is a fibrous substance in which aplurality of graphenes are arranged and layered (laminated) so as not tobe parallel to the fiber axis, as shown in FIG. 12.

On the other hand, a carbon nanotube is a fibrous substance in whichgraphenes are arranged (in cylindrical shape) around the longitudinaldirection (fiber axis direction). In other words, it is a fibroussubstance in which graphenes are arranged substantially parallel to thefiber axis.

One layer of graphite is called “graphene” or “graphene sheet”. Morespecifically, graphite is formed in such a manner that carbon planes onwhich carbon atoms are arrayed so as to form regular hexagons close toeach other by covalent bond in sp² hybridization are laid one on anotherwhile being spaced by a distance of 3.354 Å. Each carbon plane is called“graphene” or “graphene sheet”.

Each type of fibrous carbon has an electron emission threshold value ofabout 1 to 10 V/μm and is therefore preferred as the material of theemitter (electron-emitting member) 4 in accordance with the presentinvention.

In particular, electron-emitting devices using graphite nanofibers, notlimited to the device structure of the present invention shown in FIG.1, etc., are capable of causing emission of electrons in a low electricfield to obtain a large emission current, and can be readilymanufactured to obtain as an electron-emitting device having stableelectron-emitting characteristics. For example, such anelectron-emitting element can be obtained by forming graphite nanofibersas an emitter and by providing an electrode for controlling emission ofelectrons from the emitter. Further, if a light emitting member capableof emitting light when irradiated with electrons emitted from graphitenanofibers is used, a light emitting device such as a lamp can beformed. Further, an image display apparatus may be constructed byforming an array of a plurality of the above-described electron-emittingdevices and by preparing an anode having a light emitting material suchas a phosphor. In the electron-emitting device, the light emittingdevice or the image display apparatus using above-described graphitenanofibers, stable emission of electrons can be achieved withoutmaintaining inside the device or the apparatus an ultrahigh vacuum suchas that required in conventional electron-emitting devices. Moreover,since electrons are emitted by a low electric field, the device orapparatus can be easily manufactured with improved reliability.

The above-described fibrous carbon can be formed by decomposing ahydrocarbon gas by using a catalyst (a material for acceleratingdeposition of carbon). The processes for forming carbon nanotubes andgraphite nanofibers differ in the kind of catalyst and decompositiontemperature.

The catalytic material may be a material which is used as a seed forforming fibrous carbon, and which is selected from Fe, Co, Pd, No, andalloys of some of these materials.

In particular, if Pd or Ni is used, graphite nanofibers can be formed ata low temperature (not lower than 400° C.). The necessary carbonnanotube forming temperature in the case of using Fe or Co is 800° C. orhigher. Also, the process of producing a graphite nanofiber material byusing Pd or Ni, which can be performed at a lower temperature, ispreferred from the viewpoint of reducing the influence on othercomponents and limiting the manufacturing cost.

Further, the characteristic of Pd that resides in enabling oxides to bereduced by hydrogen at a low temperature (room temperature) may beutilized. That is, palladium oxide may be used as a seed formingmaterial.

If hydrogen reduction using palladium oxide is performed, an initialagglomeration seed can be formed at a comparatively low temperature(equal to or lower than 200° C.) without metallic film thermalagglomeration or ultrafine particle forming/deposition conventionallyused as ordinary seed forming techniques.

The above-mentioned hydrocarbon gas may be, for example, acetylene,ethylene, methane, propane, or propylene. Further, CO or CO₂ gas orvapor of an organic solvent such as ethanol or acetone may be used insome case.

In the device of the present invention, the region where the emitter(electron-emitting member) exists will be referred to as “emitterregion” regardless of contribution to emission of electrons.

The position of the electron emission point (electron-emitting portion)in the “emitter region” and the electron-emitting operation will bedescribed with reference to FIGS. 6 and 7.

The electron-emitting device having the distance between the cathode 3and the extraction electrode 2 to several microns was set in a vacuumapparatus 60 such as shown in FIG. 6. A sufficiently high degree ofvacuum about 10⁻⁴ Pa was produced by a evacuating pump 65. A potential(voltage Va) higher by several kilovolts than that of the cathode 3 andthe extraction electrode was applied from a voltage source (“secondvoltage application means” or “second potential application means”) tothe anode 61, which was placed so that the surface of the anode 61 is atthe height H, which was several millimeters, from the surface of thesubstrate 1, as shown in FIG. 6. While the voltage Va was appliedbetween the cathode 3 and the anode 61, the voltage applied to the anodemay be a voltage from the ground potential. The substrate 1 and theanode 61 were positioned relative to each other so that their surfacesare parallel to each other.

Between the cathode 3 and the extraction electrode 2 of theelectron-emitting device, a voltage of about several ten volts wasapplied as drive voltage Vf from a power supply (not shown) (“firstvoltage application means” or “first potential application means”).Device current If flowing between the electrodes 2 and 3 and electronemission current Ie flowing through the anode were measured.

It is supposed that, during this operation, equipotential lines 63 areformed as shown in FIG. 6 (an electric field (the direction of anelectric field) substantially parallel to the surface of the substrate1, and that the concentration of the electric field is maximized at thepoint on a portion of the electron-emitting member 4 closest to theanode and facing the gap, as indicated by 64. It is thought thatelectrons are emitted mainly from the portion of the electron-emittingmaterial in the vicinity of this electric field concentration point,where the concentration of the electric field is maximized. An Iecharacteristic such as shown in FIG. 7 was obtained. That is, Ie risesabruptly at a voltage about half the applied voltage. The Ifcharacteristic (not shown) was similar to the Ie characteristic but thevalue of If was sufficiently smaller than that of Ie.

An electron source obtained by arranging a plurality of theelectron-emitting devices in accordance with the present invention willbe described with reference to FIG. 8. In FIG. 8 are illustrated anelectron source substrate 81, X-direction wiring 82, Y-direction wiring83, electron-emitting device 84 in accordance with the presentinvention, and a connecting conductor 85.

X-direction wiring 82 has m conductors DX1, DX2, . . . DXm, which may beconstituted by, for example, a conductive metal formed by vacuumevaporation, printing, sputtering, or the like. The material, filmthickness, and width of the wiring are selected according to a suitabledesign. Y-direction wiring 83 has n conductors DY1, DY2, . . . DYn andis formed in the same manner as X-direction wiring 82. An interlayerinsulating layer (not shown) is provided between the m conductors ofX-direction wiring 82 conductors and the n conductors of Y-directionwiring 83 to electrically separate these conductors (each of m and n isa positive integer).

The interlayer insulating layer (not shown) is, for example, a SiO₂layer formed by vacuum evaporation, printing, sputtering, or the like.For example, the interlayer insulating film is formed in the desiredshape over the whole or part of the surface of the substrate 81 on whichX-direction wiring 82 has been formed and the film thickness, materialand fabrication method are selected to ensure withstanding against thepotential difference at the intersections of the conductors ofX-direction wiring 82 and Y-direction wiring 83 in particular. Theconductors of X-direction wiring 82 and Y-direction wiring 83 arerespectively extended outward as external terminals.

Pairs of electrodes (not shown) constituting electron-emitting devices84 are electrically connected to the m conductors of X-direction wiring82 and the n conductors of Y-direction wiring 83 by connectingconductors 85 made of a conductive metal or the like.

The materials forming wiring 82 and wiring 83, the material forming theconnecting conductors 85 and the materials forming the pairs of deviceelectrodes may be entirely constituted of common constituent elements orpartially constituted of common constituent elements, or may beconstituted of different constituent elements. These materials areselected from, for example, the above-described device electrodematerials. If the materials of the device electrodes and the wiringmaterials are the same, the wiring conductors connected to the deviceelectrodes can be considered to be device electrodes.

A scanning signal application means (not shown) for applying scanningsignals for selecting the rows of electron-emitting devices 84 arrangedin the X-direction is connected to X-direction wiring 82. On the otherhand, a modulation signal generation means for modulating voltagesapplied to the columns of electron-emitting devices 84 arranged in theY-direction according to input signals is connected to Y-directionwiring 83. The drive voltage applied to each electron-emitting device issupplied as a voltage corresponding to the difference between thescanning signal and the modulation signal applied to the element.

In the above-described arrangement, each device can be selected by usingthe passive-matrix wiring to be driven independently.

An image forming apparatus constructed by using an electron sourcehaving such a passive matrix array will be described with reference toFIG. 9. FIG. 9 schematically shows an example of the display panel ofthe image forming apparatus. Referring to FIG. 9, a plurality ofelectron-emitting devices are disposed on an electron source substrate81, which is fixed on a rear plate 91. A face plate 96 has a glasssubstrate 93, a phosphor film 94 provided as a light emitting member onthe internal surface of the glass substrate 93, a metal back (anode) 95,etc. The rear plate 91 and the face plate 96 are connected to asupporting frame 92 by using frit glass or the like. An envelop 97 isformed by being seal-bonded by baking in, for example, atmospheric air,a vacuum or in nitrogen in the 400 to 500° C. temperature range for 10minutes or longer.

The envelop 97, as described above, is constituted by the face plate 96,the supporting frame 92, and the rear plate 91. The rear plate 91 isprovided mainly for the purpose of reinforcing the substrate 81. If thesubstrate 81 itself has sufficiently high strength, there is no need toseparately provide the rear plate 91. That is, the supporting frame 92may be directly seal-bonded to the substrate 81 and the envelop 97 maybe formed by the frame plate 96, the supporting frame 92 and thesubstrate 81. A supporting member (not shown) called a spacer may beprovided between the face plate 96 and the rear plate 91 to enable theenvelop 97 to have a sufficiently high strength for resistingatmospheric pressure.

Embodiments of the present invention will be described below in detail.

Embodiment 1

FIG. 1A shows a top view of an electron-emitting device fabricated inthis embodiment. FIG. 1B is a cross-sectional view taken along the line1B-1B of FIG. 1A.

FIGS. 1A and 1B illustrate an insulating substrate 1, an extractionelectrode 2 (gate), a cathode 3, and an emitter material 4.

The process of fabricating the electron-emitting device of thisembodiment will be described in detail.

(Step 1)

A quartz substrate was used as substrate 1. After sufficiently cleansingthe substrate, a 5 nm thick Ti film (not shown) and a 30 nm thickpoly-Si film (arsenic doped) were successively deposited by sputteringon the substrate as gate electrode 2 and cathode 3.

Next, a resist pattern was formed by photolithography using a positivephotoresist (AZ1500/ from Clariant Corporation).

Thereafter, dry etching was performed on the poly-Si (arsenic doped)layer and Ti layer with the patterned photoresist used as a mask, CF₄gas being used to etch the Ti layer. An extraction electrode 2 and acathode 3 having a gap of 5 μm therebetween were thereby formed (FIG.5A).

(Step 2)

Next, a Cr having a thickness of about 100 nm was deposited on theentire substrate by electron beam (EB) evaporation.

A resist pattern was formed by photolithography using a positivephotoresist (AZ1500/ from Clariant Corporation).

An opening corresponding to a region (100 μm square) whereelectron-emitting material 4 was to be provided was formed on thecathode 3 with the patterned photoresist used as a mask. Cr at theopening was removed by using a cerium nitrate etching solution.

After removing the resist, a complex solution prepared by addingisopropyl alcohol, etc., to a Pd complex was applied to the entiresubstrate by spin coating.

After application of the solution, a heat treatment was performed inatmospheric air at 300° C. to form a palladium oxide layer 51 having athickness of about 10 nm. Thereafter, Cr was removed by using a ceriumnitrate etching solution (FIG. 5B).

(Step 3)

The substrate was baked at 200° C., atmospheric air was evacuated, and aheat treatment was then performed in 2% hydrogen flow diluted withnitrogen. At this stage, particles 52 having a diameter of about 3 to 10nm were formed on the surface of the cathode 3. The density of theparticles at this stage was estimated at about 10¹¹ to 10¹²particles/cm² (FIG. 5C).

(Step 4)

Subsequently, a heat treatment was performed in a 0.1% ethylene flowdiluted with nitrogen at 500° C. for 10 minutes. The state after theheat treatment was observed with a scanning electron microscope to findthat a multiplicity of fibrous carbon 4 having a diameter of about 10 to25 nm and extending like fibers while curving or bending had been formedin the Pd-coated region. The thickness of the fibrous carbon layer wasabout 500 nm (FIG. 5D).

This electron-emitting device was set in the vacuum apparatus 60 shownin FIG. 6. A sufficiently high vacuum of about 2×10⁻⁵ Pa was produced bythe evacuating pump 62. Voltage Va=10 kV was applied as anode voltage tothe anode 61 distanced by H=2 mm from the device, as shown in FIG. 6.Also, a pulse voltage of Vf=20 V was applied as drive voltage to thedevice. Device current If and electron emission current Ie therebycaused were measured.

The If and Ie characteristics of the electron-emitting device were asshown in FIG. 7. That is, Ie rises abruptly at a voltage about half theapplied voltage, and a current of about 1 μA was measured as electronemission current Ie at a Vf value of 15 V. On the other hand, the Ifcharacteristic was similar to the Ie characteristic but the value of Ifwas smaller than that of Ie by an order of magnitude or more.

The obtained beam had a generally rectangular shape having a longer sidealong the Y-direction and a shorter side in the X-direction. The beamwidth was measured with respect to different gaps of 1 μm and 5 μmbetween the electrodes 2 and 3 while Vf was fixed at 15 V and thedistance H to the anode was fixed at 2 mm. Table 1 shows the results ofthis measurement.

TABLE 1 Va = 5 kV Va = 10 kV Gap: 1 μm  60 μm in x-direction  30 μm inx-direction 170 μm in y-direction 150 μm in y-direction Gap: 5 μm  93 μmin x-direction  72 μm in x-direction 170 μm in y-direction 150 μm iny-direction

It was possible to change the necessary electric field for driving bychanging the fibrous carbon growth conditions. In particular, theaverage particle size of Pd particles formed by reduction of palladiumoxide is related to the diameter of fibrous carbon thereafter grown. Itwas possible to control the average Pd particle size through the Pddensity in the Pd complex coating and the rotational speed of spincoating.

The fibrous carbon of this electron-emitting device was observed withthe transmission electron microscope to recognize a structure in whichgraphenes are layered in the fiber axis direction, as shown in theright-hand section of FIG. 12. The graphene stacking intervals (in theZ-axis direction) resulting from heating at a lower temperature, about500° C. were indefinite and was 0.4 nm. As the heating temperature wasincreased, the grating intervals became definite. The intervalsresulting from heating at 700° C. were 0.34 nm, which is close to 0.335nm in graphite.

Embodiment 2

FIG. 2 shows a second embodiment of the present invention.

In this embodiment, an electron-emitting device was fabricated in thesame manner as that in the first embodiment except that the cathode 3corresponding to that in the first embodiment had a thickness of 500 nmand fibrous carbon provided as electron-emitting material 4 had athickness of 100 nm. Currents If and Ie in the fabricatedelectron-emitting device were measured.

In this device arrangement, the electron emission point was positivelyheightened (toward the anode) relative to the gate electrode byincreasing the thickness of the cathode 3. Trajectories along whichelectrons impinge on the gate were thereby reduced, thereby preventing areduction in efficiency and occurrence of a beam-thickening phenomenon.

Also in this device arrangement, the electron emission current Ie atVf=20V was about 1 μA. On the other hand, the If characteristic wassimilar to the Ie characteristic but the value of If was smaller thanthat of Ie by two orders of magnitude.

The results of measurement of the beam diameter in this embodiment weresubstantially the same as those shown in Table 1.

Embodiment 3

FIG. 3 shows a third embodiment of the present invention.

In this embodiment, in the step corresponding to step 2 in the firstembodiment, palladium oxide 51 was provided on the cathode 3 and in thegap between the electrodes 2 and 3. Pd oxide was provided in the gap insuch a manner as to extend from the cathode 3 to a point near themidpoint of the gap. Excepting step 2, this embodiment is the same asthe first embodiment.

The electric field in the electron-emitting device of this embodimentwas twice as strong as that in the first embodiment because the gap wasreduced, thereby enabling the drive voltage to be reduced to about 8 V.

Embodiment 4

FIG. 4 shows a fourth embodiment of the present invention. In thisembodiment step 1 and step 2 described above with respect to the firstembodiment are changed as described below.

(Step 1)

A quartz substrate was used as substrate 1. After sufficiently cleansingthe substrate, a 5 nm thick Ti film and a 30 nm thick poly-Si film(arsenic doped) were successively deposited by sputtering on thesubstrate as cathode 3.

Next, a resist pattern was formed by photolithography using a positivephotoresist (AZ1500/ from Clariant Corporation).

Next, dry etching was performed on the poly-Si layer and Ti layer byusing CF₄ gas, with the patterned photoresist used as a mask. Cathode 3was thereby formed.

The quartz substrate was then etched to a depth of about 500 nm by usinga mixed acid formed of hydrofluoric acid and ammonium fluoride.

Subsequently, a 5 nm thick Ti film and a 30 nm thick Pt film weresuccessively deposited on the substrate as gate electrode 2 by againperforming sputtering. After removing the photoresist from the cathode,a resist pattern was again formed by using a positive photoresist(AZ1500/ from Clariant Corporation) to form the gate electrode.

Next, dry etching was performed on the Pt layer and Ti layer by usingAr, with the patterned photoresist used as a mask. Electrode 2 wasthereby formed so that the step formed between the electrodes functionsas a gap.

Next, a resist pattern was formed on the cathode, a Ni film having athickness of about 5 nm was formed by resistance heating evaporationhaving a good straight-in effect, and oxidation was thereafter performedat 350° C. for 30 minutes.

This step was followed by the same steps as those in the firstembodiment.

The above-described device arrangement enabled formation of a finer gapsuch that electrons were effectively emitted at a lower voltage of about6 V.

Because the height of the electron-emitting material 4 (film thickness)was increased relative to that of the gate electrode, electrons weredrawn out not only from the upper portion of the electron-emittingmaterial 4 but also from an intermediate portion. Thus, the arrangementin this embodiment has the effect of preventing a reduction inefficiency due to impingement of electrons on the gate electrode andoccurrence of a beam-thickening phenomenon.

Embodiment 5

An electron source obtained by arranging a plurality of theelectron-emitting devices fabricated the first embodiment and an imageforming apparatus using this electron source will be described withreference to FIGS. 8, 9, and 10. In FIG. 8 are illustrated an electronsource substrate 81, X-direction wiring 82, Y-direction wiring 83,electron-emitting devices 84 in accordance with the present invention,and connecting conductors 85.

The electron source with matrix wiring shown in FIG. 8, in which thedevice capacitance is increased by arranging a plurality ofelectron-emitting devices, has a problem that, even when a short pulseproduced by pulse-width modulation is applied, the waveform is dulled ordistorted by capacitive components to cause failure to obtain thenecessary grayscale level, for example. In this embodiment, therefore, astructure is adopted in which an interlayer insulating layer is providedby the side of the electron-emitting region to limit the increase incapacitive components in regions other than the electron-emittingregion.

Referring to FIG. 8, X-direction wiring 82 has m conductors DX1, DX2, .. . DXm, which has a thickness of about 1 μm and a width of 300 μm, andwhich is formed of an aluminum wiring material by evaporation. Thematerial, film thickness, and width of the wiring conductors areselected according to a suitable design. Y-direction wiring 83 has nconductors DY1, DY2, . . . DYn, which has a thickness of 5 μm and widthof 100 μm, and which is formed in the same manner as X-direction wiring82. An interlayer insulating layer (not shown) is provided between the mconductors of X-direction wiring 82 and the n conductors of Y-directionwiring 83 to electrically separate these conductors (each of m and n isa positive integer).

The interlayer insulating layer (not shown) is, for example, a SiO₂layer formed by sputtering or the like and having a thickness of about0.8 μm. For example, the interlayer insulating film is formed in thedesired shape over the whole or part of the surface of the substrate 81on which X-direction wiring 82 has been formed. Specifically, thethickness of the interlayer insulating film is determined so as toensure withstanding against the potential difference at theintersections of the conductors of X-direction wiring 82 and Y-directionwiring 83. The conductors of X-direction wiring 82 and Y-directionwiring 83 are respectively extended outward as external terminals.

Pairs of electrodes (not shown) constituting electron-emitting devices84 are electrically connected to the m conductors of X-direction wiring82 and the n conductors of Y-direction wiring 83 by connectingconductors 85 made of a conductive metal or the like.

A scanning signal application means (not shown) for applying scanningsignals for selecting the rows of electron-emitting devices 84 arrangedin the X-direction is connected to X-direction wiring 82. On the otherhand, a modulation signal generation means for modulating voltagesapplied to the columns of electron-emitting devices 84 arranged in theY-direction according to input signals is connected to Y-directionwiring 83. The drive voltage applied to each electron-emitting device issupplied as a voltage corresponding to the difference between thescanning signal and the modulation signal applied to the element. In thepresent invention, Y-direction wiring 83 is connected to the gateelectrodes 2 of the electron-emitting devices described above withrespect to the first embodiment, while X-direction wiring is connectedto the cathodes 3 of the elements. This connection realizes a beamconvergence effect which characterizes the present invention.

In the above-described arrangement, each element can be selected byusing the passive-matrix wiring to be driven independently.

An image forming apparatus constructed by using an electron sourcehaving such a passive matrix array will be described with reference toFIG. 9. FIG. 9 is a diagram showing the display panel of the imageforming apparatus.

Referring to FIG. 9, the electron source having the plurality ofelectron-emitting devices described above with reference to FIG. 8 isprovided on an electron source substrate 81. The substrate 81 is fixedon a rear plate 91. A face plate 96 has a glass substrate 93, a phosphorfilm 94 provided as a light emitting member on the internal surface ofthe glass substrate 93, a metal back 95, etc. The rear plate 91 and theface plate 96 are connected to a supporting frame 92 by using frit glassor the like. An envelop 97 is formed by being seal-bonded by baking in avacuum at about a temperature of 450° C. for 10 minutes. Theelectron-emitting devices 84 correspond to the electron-emitting regionsshown in FIG. 9. X-direction wiring 82 and Y-direction wiring 83 areconnected to the pairs of electrodes of the electron-emitting elementsin this embodiment.

The envelop 97, as described above, is constituted by the face plate 96,the supporting frame 92, and the rear plate 91. A supporting member (notshown) called a spacer is provided between the face plate 96 and therear plate 91 to enable the envelop 97 to have a sufficiently highstrength for resisting atmospheric pressure.

After fabrication of the phosphor film, the metal back 95 is made bysmoothing the inner surface of the phosphor film (ordinarily called“filming”) and by thereafter depositing Al by vacuum evaporation or thelike.

The face plate 96 further has a transparent electrode (not shown)provided on outer surface of the phosphor film 94 to improve theconductivity of the phosphor film 94.

The scanning circuit 102 will be described. The scanning circuit 102includes M switching devices (schematically shown as S1 to Sm in thefigure). Each of the switching devices S1 to Sm selects one of theoutput voltage from a direct-current voltage source Vx and 0 (V) (groundlevel). The switching devices S1 to Sm are respectively connected toterminals Dx1 to Dxm of the display panel 101. Each of the switchingdevices Si to Sm operates on the basis of a control signal Tscan outputfrom a control circuit 103, and may be a combination of a switchingdevice such as a field-effect transistor (FET) and other components. Inthis example, the direct-current voltage source Vx is configured tooutput a constant voltage such that the drive voltage to be applied to adevice which is not scanned on the basis of characteristics of theelectron-emitting device (electron emitting threshold value voltage), isnot higher than the electron-emitting threshold value voltage.

The control circuit 103 has the function of matching the operations ofthe components with each other to suitably perform display on the basisof input signals externally supplied. The control circuit 103 generatescontrol signals Tscan, Tsft, and Tmry to the components on the basis ofsync signal Tsync supplied from a sync signal separation circuit 106.

The sync signal separation circuit 106 is a circuit for separating syncsignal components and luminance signal components from an NTSCtelevision signal externally supplied. This circuit can be formed byusing an ordinary frequency separation (filter) circuit, etc. The syncsignal separated by the sync signal separation circuit 106 is formed ofa vertical sync signal and a horizontal sync signal. However, it isshown as Tsync in the figure for convenience sake. Image luminancesignal components separated from the television signal are shown as DATAsignal for convenience sake. The DATA signal is input to a shiftregister 104.

The shift register 104 is a device for serial to parallel conversion,with respect to each image line, of the DATA signal which is input intime sequence. The shift register 104 operates on the basis of controlsignal Tsft supplied from the control circuit 103. (That is, controlsignal Tsft may be considered to be a shift clock for the shiftregister.) Data corresponding to one image line after serial to parallelconversion (corresponding to data for driving N electron-emittingdevices) is output as N parallel signals Id1 to Idn from the shiftregister 104.

The line memory 105 is a storage device for storing data correspondingto one image line for a necessary time period. The line memory 105stores the contents of the signals Id1 to Idn according to controlsignal Tmry supplied from the control circuit 103. The stored contentsare output as I'd1 to I'dn to be input to a modulation signal generator107.

The modulation signal generator 107 is a signal source for suitablymodulating signals for driving the electron-emitting devices accordingto image data items I'd1 to I'dn. Output signals from the modulationsignal generator 107 are applied to the electron-emitting devices in thedisplay panel 111 through terminals Doy1 to Doyn.

As described above, each electron-emitting device to which the presentinvention can be applied has basic characteristics described below withrespect to emission current Ie. That is, there is a definite thresholdvalue voltage Vth with respect to emission of electrons. Emission ofelectrons is caused only when a voltage higher than Vth is applied. Whena voltage higher than the electron emission threshold value is appliedto the electron-emitting device, the emission current changes accordingto changes in the applied voltage. Therefore, in a case where a voltagein the form of pulses is applied to the electron-emitting device,electron emission is not caused when the value of the applied voltage islower than the electron emission threshold value, but an electron beamis output when the value of the applied voltage is equal to or higherthan the electron emission threshold value. In this case, the strengthof the electron beam can be controlled by changing the pulse crest valueVm. Also, the total amount of charge of the output electron beam can becontrolled by changing the pulse width Pw.

Therefore, a voltage modulation method, a pulse-width modulation methodor the like can be used as a method for modulating the electron-emittingdevice according to the input signal. If the voltage modulation methodis carried out, a voltage modulation type of circuit capable ofgenerating voltage pulses having a constant duration, and modulating thepulse crest value according to input data may be used as modulationsignal generator 107.

If the pulse-width modulation method is carried out, a pulse-widthmodulation type of circuit capable of generating voltage pulses having aconstant crest value and modulating the pulse width of the voltagepulses according to input data may be used as modulation signalgenerator 107.

Each of the shift register 104 and the line memory 105 used in thisembodiment is of a digital signal type.

In this embodiment, a digital to analog converter circuit, for example,is used in the modulation signal generator 107 and an amplifier circuit,etc., are added if necessary. For example, in the case where thepulse-width modulation method is used, a combination of a high-speedoscillator, a counter for counting the number of waves output from theoscillator, and a comparator for comparing the output value of thecounter and the output value of the above-described memory is used inthe modulation signal generator 107.

The configuration of the image forming apparatus described above is anexample of the image forming apparatus to which the present inventioncan be applied. Various modifications and changes can be made therein onthe basis of the technical spirit of the present invention. The inputsignal is not limited to the above-mentioned NTSC signal. Those inaccordance with the PAL system and the SECAM system and other TV signalscorresponding to a larger number of scanning lines (e.g., those for theMUSE system and other high-definition TV systems) may also be used.

Images were displayed on an image display apparatus made in accordancewith this embodiment. High-luminance high-definition images had beendisplayed on the image display apparatus with stability for a longperiod of time.

According to the present invention, as described above, the specificcapacitance of an electron-emitting device can be reduced and the drivevoltage can also be reduced. An electron source having improvedefficiency and a smaller beam size can be realized by using such anelectron-emitting device.

An image forming apparatus having high resolution, e.g., a colorflat-screen television can be realized by using the electron-emittingdevice in accordance with the present invention.

1. An electron-emitting apparatus comprising: (a) an anode electrode;(b) a cathode electrode and a gate electrode, which are arranged at aninterval so as not to be overlapped with each other, directly on a flatsurface of an insulating substrate opposed to said anode electrode; and(c) a plurality of carbon fibers, arranged on said cathode electrode andconnected electrically to said cathode electrode, wherein each of saidcarbon fibers has a plurality of graphenes which are aligned so as notto be parallel to an axis-direction of said fiber, and wherein saidgraphenes are stacked in said axis-direction.
 2. The electron-emittingapparatus according to claim 1, wherein the electron-emitting device isarranged in opposition to an anode electrode at a driving thereof, andthe plurality of carbon fibers have a portion which is positioned at ashorter distance from the anode electrode rather than a distance betweenthe anode electrode and the gate electrode.
 3. The electron-emittingapparatus according to claim 1, wherein the cathode electrode and thegate electrode are arranged on the same surface of the substrate.
 4. Theelectron-emitting apparatus according to claim 1, wherein the cathodeelectrode and the gate electrode have the same thickness.
 5. Theelectron-emitting apparatus according to claim 1, wherein a distancebetween the portion of the carbon fiber and the surface of the substrateis longer than a distance between a surface of the gate electrode andthe surface of the substrate.